Monoclonal antibodies (Mabs) have been widely used in diagnostics, and there is a growing interest in their use in human therapy. Although the original and still most successful procedure for generating Mabs is by way of mouse-cell hybridomas, mouse Mabs have a number of limitations, both in diagnostic and therapeutic uses.
In the diagnostics area, it would be extremely valuable, in diagnosing propensity to disease and for purposes of transplantation or transfusion matching, to be able to recognize many of the polymorphisms in human cell surface alloantigens, e.g., histocompatibility antigens. Efforts to obtain mouse Mabs which are specific against individual polymorphisms, such as red blood cell alloantigens and histocompatibility antigens have had only very limited success, because the immunized mice appear to preferentially react immunologically to species-specific "backbone" determinants that are shared by all such antigens, rather than to the polymorphic determinants that vary among individuals of a population. Ideally, one would like to produce the polymorphic-specific Mabs in a non-human primate, such as the chimpanzee, which is phylogenetically close to humans, and which would therefore be expected to share many of the same antigenic backbone determinants with humans.
In some human diseases for which Mab-based diagnosis would be valuable, such as hepatitis nonA/nonB (NANB), the infective agent(s) has not been identified and, therefore, mouse B lymphocytes specific against the agent have not yet been obtained. In this example, the only known biological assay of NANB infectivity is transmission to chimpanzees (reference 1). For this reason and with this particular agent, as well as others for which antigen-specific human B lymphocytes also have not yet been obtained, it would be desirable to be able to produce Mabs using sensitized B lymphocytes obtained from infected non-human primates.
In the therapeutics area, mouse Mabs are expected to be of limited value, especially where multiple injections of the antibody must be given, because of the likelihood that the patient will develop a severe immunological response to the foreign antibodies. Although the immune response problem may be solved by use of human Mabs, there are also significant limitations associated with deriving humabn Mabs against many selected antigens. One of the limitations which has been encountered in producing human Mabs is in immortalizing human B lymphocytes in a manner that leads to stable antibody-producing cell lines. Heretofore, two major approaches for producing human Mab-secreting cells have been used: direct immortalization of immunized lymphocytes with Epstein-Barr Virus (EBV) and Mab production by hybridomas formed between immortalized human B cell lines (EBV), lymphoblastoid, or human or murine myelomas, and human B lymphocytes from an immunized host. Neither of these approaches has proved entirely satisfactory.
It is common experience among practitioners in the art that EBV transformation, while successful in forming Mab-secreting cultures, will often fail to provide antigen-specific EBV transformed cells which have sufficiently long life spans to provide reliable sources of the desired antibodies (reference 2). Thus, this method fails to provide reliably for antibody production over extended periods. Previously produced hybridomas between immunized human B cells and appropriately drug marked mouse or human myeloma or human lymphoblastoid cell lines have suffered from low frequency of hybrid formation in the case of human-human hybridizations (reference 3) or chromosomal instability in the case of murine-human hybridomas (references 4 and 5).
The problem of producing a stable, human Mab-producing cell line has been addressed by the inventors in the above co-pending application of A Novel Fusion Partner and Products. Briefly, it was discovered that stable, human Mab-secreting cell lines could be produced by (a) constructing a mouse myeloma/human lymphocyte hybridoma cell line having certain selected-for characteristics, and (b) fusing the hybridoma with a human B lymphocyte from an individual immunized with a selected antigen. The method disclosed in the above co-pending application is described generally in reference 6. Relevant aspects of the trioma-cell invention will be given below.
Although the above trioma method can be used to generate stable, human Mab-secreting cells, it is limited, as are the other human Mab methods mentioned above, to antibodies for which active B lymphocytes are available from human donors. In many cases, it is either not possible to immunize humans, e.g., where toxins, active viruses, or the like are involved, or it is difficult to identify individuals that have been recently immunized to the antigen of interest.
An alternative source of B lymphocytes for use in producing Mabs suitable for human therapy are non-human primates. Mabs from primates, such as the chimpanzee, which are phylogenetically similar to humans would be much less likely to cause an anti-immunoglobulin response to humans that would Mabs from a source such as mice. At the same time, the animals could be immunized with a variety of antigens which cannot be administered to humans, and the antigen-specific B lymphocytes could be obtained at an optimal time after immunization. For the agent(s) responsible for NANB hepatitis, chimpanzees are the only experimental animals known to be susceptible to this disease.